In the field of wireless data communication the transmission media includes electromagnetic radiation transmission in the radar, radio and microwave frequency ranges. The transmitting and receiving apparatus typically include dish or dipole type antennae.
Wireless data transmission using reflected infrared radiation is disclosed in our copending U.S. patent application Ser. No. 184,261. It is preferable that inexpensive commercially available infrared LEDs be used as the transmission source for the infrared radiation. However, the intensity of such LEDs is generally insufficient to effectively transmit intelligible radiation for useful distances. To overcome this problem multiple LEDs may be employed. Each additional LED increases the intensity of the transmitted radiation.
For connecting multiple infrared transceivers together, such as for a local area network (LAN) in an open office environment, acoustical ceiling tile makes an ideal diffuse infrared reflector. In a large open office environment, of the type using cubicle offices, the ideal illumination size on the diffuse infrared reflector is an area having maximum dimensions of eight to ten feet. Having an illuminated location of this size will allow for the inherent variations in illumination size which results from the relative location of each transceiver.
In a large open office it is preferable that the illumination location be somewhat centralized. For a single open office having more than one LAN two or more illumination spots are necessary. Clearly, each of these illumination spots cannot be in the center of the room. As infrared illumination is transmitted, the radiation beam will spread out as the distance increases. Thus, those transceivers positioned directly below the illumination location will project a relatively small spot and those transceivers positioned across the room will project a larger spot.
In a large room having cubicles, the angle of an incident radiation beam can become quite small. If the ceiling is twelve feet off the floor and transceiver is mounted on top of a five foot cubicle wall a beam projected from forty feet away forms an average angle of approximately ten degrees to the ceiling. If the LEDs are tightly clustered or in a vertical orientation in the transmitter the projected pattern becomes a long thin stripe on the ceiling. FIG. 1 shows an infrared transmitter 10 in a room 12 projecting an infrared signal at the ceiling. The transmitter 10 has a plurality of infrared LEDs positioned in a line. The orientation of the line of LEDs is essentially vertical. The illumination projection 14 is shown as a long stripe on the ceiling.
What is needed is a infrared transmitter which will transmit an infrared signal at relatively small projection angels and still maintain a small compact illumination location.